Download The future sun March 18 −

• Why does the sun die?
• What will the sun become
when it dies?
• Fri & Sat, 9-11pm, if it is
not cloudy.
• Mar 18 & 19
• Apr 15 & 16
• May 13 & 14
• 24-inch telescope in dome
• small telescopes outside
Star cluster Pleiades
• Evidence on giants from star
clusters
• All stars in a cluster are born at
once.
• 100,000 fraternal twins, some
weighing 30 times me, the G
star, some 1/10 me.
1e6
1e4
→
• New policy: if you turn in
more than 2 clicker paper
answers, they will count 2
pts/question.
• Public viewing sessions at
MSU campus observatory.
Giants are dying stars; white dwarfs are dead stars
100
1
Luminosity
The future sun−March 18
0.01
1e-4
30,000
10,000 6,000
Temperature
3,000
HR Diagram of Clusters
• Not all fainter stars
were observed
• In what ways are
HR diagrams of
H+χ Perseus,
Pleiades, Hyades, &
NGC188 different?
• Perseus is hotter
than Pleiades
• Not all stars are
on MS
• Perseus has small
range of
luminosity
1
HR Diagram of Clusters
106
O star: 30M¤; 200,000L¤
Lifetime=amount of fuel/consumption rate
Lifetime=21gallons/(3gallons/hr)=7hr
Lifetime=30M¤/ 200,000L¤
=Lifetime¤/7000 =1.3Myr
Human scale = 4days
→
104
Luminosity
• In what ways are
HR diagrams of
H+χ Perseus,
Pleiades,
Hyades, &
NGC188
different?
Stars with high mass live a short life
102
100
10-2
Sun
Lifetime=10Byr
Human scale 80yr
Barnard’s star: 0.1M¤; 0.004L¤
10-4
Lifetime=0.1M
¤/ 0.004L¤
=25Lifetime¤ =250Byr
Human scale = 20,000yr
25,000
H-R Diagrams of star clusters
1. There are no A stars in
M80 because
a. they never formed.
b. they died and disappeared
c. all stars became redder as
they get older.
d. they are too faint to see.
10,000
5,000
Temperature
3,000
H-R Diagrams of star clusters
2. The hottest dwarfs in
Pleiades are A stars. The
hottest dwarfs in M15 are
F stars. Pleiades is ___
than M15.
a. older
b. younger
2
Life of the sun
•
•
•
•
Life of the sun
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
è Red
•
•
•
•
giant.
è Red
HèHe burning
core
Inert H
ç Temperature
Inert He core
ç Temperature
•
•
•
•
Life of the sun
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
è Red
•
•
•
•
giant.
HèHe burning
shell
Inert H
giant.
Later
Luminosity è
Luminosity è
Inert He core
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
è Red
Few 100 Myr later
ç Temperature
HèHe burning
shell
Inert H
Radius
photosphere
Life of the sun
Radius
photosphere
giant.
5 Byr from now
Luminosity è
Luminosity è
Present sun
Radius
photosphere
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
Inert He core
Radius
photosphere
HèHe burning
shell
Inert H
ç Temperature
3
After helium is used up
Reaction
Min. Temp.
107 o K
3 4He è 12C
+
4He
è
2x108
16O,
Ne, Na, Mg
8x108
Ne è O, Mg
1.5x109
O è Mg, S
2x109
Si èFe peak
3x109
Triple-alpha process
Min. Temp.
4 1H è 4He
107 o K
3 4He è 12C
2x108
12C
4 1H è 4He
12C
Reaction
+ 4He è 16O, Ne, Na, Mg
8x108
• Mg
Following He è C, O
Ne è O,
for 9
O è Mg, Score never gets hot enough2x10
further reactions.
Si èFe peak
3x109
Planetary nebula
shell expelled.
burning,
1.5x109
Stars with < 2 M•
• End is He à C, O burning.
• Core never gets hot enough
for further reactions.
• Contraction heats
center
• Helium starts to burn.
Star continues to
shrink. Surface
becomes very hot.
[Fig. 12.10]
Solar-mass star
4